Infrared detectors for middle- and far-infrared bands (for example, bands of wavelengths from 3 μm to 12 μm) which have been put into practical use include: a detector using HgCdTe which is a group II-VI compound semiconductor; a QWIP (Quantum Well Infrared Photo-detector) using a superlattice of group III-V compound semiconductors (for example, GaAs/AlGaAs or the like); and a QDIP (Quantum Dot Infrared Photo-detector) using a quantum dot.